Cement choices

Our guest bathroom has a concrete slab floor. It’s tiled over with 12X18 grey ceramic tiles. They tiled around the vanity.

I tore out the rotten 1959 wood vanity.

The new vanity is free standing on 4" tall stubby feet; just enough to vacuum under.

I suppose I could search for a matching tile and grout to fill the untiled footprint of the old vanity, or I could simply fill it with a smooth concrete (since it won’t really be visible under the new vanity).

What kind of mortar or cement to get a reallly smooth surface? It’s always about 60f in that room; never too hot or cold.

“The different types of mortar are denoted by the letters: M, S, N, and O”.

… and how much to fill the space that’s 1/2" deep x 15" x 36" ?

I know there’s self-leveling mortar–fairly runny stuff that dries hard quickly–for use as underlayment for tiling jobs. Would probably work. E.g.,
https://www.lowes.com/pd/Henry-565-FloorPro-Self-Leveling-Un…

But I’d probably go with trying to find some tile, either a very close match or perhaps a contrasting color or style. Some years ago, a friend of mine who is an interior designer faced a similar problem. He ended up carefully removing some of the old tiles in a semi-random pattern, used them to replicate the pattern in the untiled space, and then filled the holes with nice contrasting tiles.

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I’ll second the self leveling. Works quite well, gets very smooth, but it has to be level, since it will utilize gravity, and will be level, even if your floor isn’t. If your floor is level, you are probably looking at 1 bag to fill that space.

Another option would be non shrink grout. It is quite hard, and can be troweled, but the level is up to you.

Normal mortar would work, but isn’t designed for that type of application. It would likely shrink and give you cracks. It is designed for joints in masonry, and shouldn’t be utilized as a flat surface, although some do so.

I’ll second the self leveling. Works quite well, gets very smooth, but it has to be level, since it will utilize gravity, and will be level, even if your floor isn’t. If your floor is level, you are probably looking at 1 bag to fill that space.

There are different levels of “self-leveling” and I don’t know how to tell you the difference. I’ve used one kind of cement which is “sort of” self leveling but still leaves some modestly uneven parts, small ripples, that sort of thing. And I’ve used another which is made for underpayment of wood floors which levels like water to a near-glass sheen although it’s a bit more viscous than that.

If that’s the route you go I would suggest doing a small test area someplace, even on a 1x1 board with temporary edges to see how it comes out. Once you put it down it’s devilishly hard to level up after it dries.

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I agree with the other poster that putting tile in that spot is your best option.
Even if you go with just tiling that section with similar color 12x12 or 12x18 grey tiles it will IMO look far better than any cement or mortar infill you do.

Even if it’s not fully matching tile and grout, it’s still a better option than self-leveling concrete or mortar or anything similar.

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The guy at Ace gave me a torn 60 pound sack of Quickcrete mortar.

"Quikrete 60 lbs. mortar mix consists of a uniformly blended mixture of fine sand and type N masonry cement and can be used for laying brick, block or stone. It can be used for above grade and non-load bearing work with brick, stone and block. Quikrete 60 lbs. mortar mix is the perfect mix for your everyday masonry projects.
Use for construction and repair of brick, block and stone
Perfect for masonry projects that are not load bearing
750 psi compression strength
Meets ASTM C 270 for type N mortar

It may be a case of ‘you get what you pay for’, but I’ll do a small test batch in a frame on the garage floor in the morning anyway.

Well you already have the QuickCrete so that’s worth a test.

Thinking about it I would probably try to find a complimentary colored tile (you will never match the original, nor the grout. Life is like that.) and do the patch as though it was designed to be the underlayment for the cabinet.

Do your best to match - or make slightly higher - the new section; you don’t want it to be a “well” for spilled water. I have a leveling “puck” to check for level, but you could use any hard sided instrument; a pot or a pan or whatever, just slide it back and forth until you don’t hear the “click” anymore. There are new “tile leveler” plastic thingies you put at the edges which allow you to pull a tile “up” to level, if necessary; then they break off. Didn’t have those back when I was doing a lot of this.

As GWP noted earlier, get some plastic feet and put them under the cabinet; a friend failed to do so even after I mentioned it, and after a single spill the water wicked up into the wood of his cabinet and made it look pretty crappy. Just keeping the legs 1/8 or 1/4 inch off the floor will prevent that.

get some plastic feet and put them under the cabinet

I got some tiles that are almost the same color. Since they’ll be under the vanity, nobody will really notice the slight variation. Close enough for army work.

Good idea, plastic under the vanity legs. I’m thinking 4 HDPE caps from milk containers, hot glued to the bottoms of the feet.

I’m thinking 4 HDPE caps from milk containers, hot glued to the bottoms of the feet.

Or for $1.18 you can get a set that will never unglue:

https://www.homedepot.com/p/Shepherd-1-1-8-in-White-Round-Fe…

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